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Independent Laboratory Observations
2
3
The results of this study demonstrate the ability of the MDA 2 -
Listeria
to detect the presence of
4
Listeria
in various food matrixes and select environmental surfaces after 24-28 hours of a
5
primary enrichment. The MDA 2 -
Listeria
offers the benefits of extremely high sensitivity and
6
high specificity for the detection of
Listeria
while reducing the overall time to presumptive
7
results. The MDA 2 -
Listeria
also reduces the total analyst time required to obtain final results
8
by implementing a single heat lysis step and cool step, followed up by a single transfer to
9
molecular reaction tubes. The small footprint of the Molecular Detection System requires only
10
minimal lab and bench space, making it easy to move the instrument or pair up additional MDS
11
units to perform multiple MDA runs concurrently. The updated software is user friendly with
12
easy to interpret results. The ability to examine Relative Light Unit (RLU) curves makes trouble
13
shooting more streamlined if any problems occur while testing is being conducted.
14
15
Discussion
16
17
All matrixes evaluated in this validation study, including the raw chicken, resulted in no
18
statistical differences when compared to the reference methods. Three different brands of Demi
19
Fraser with FAC were used in this study, referred to as X, Y, and Z.
20
21
There were no differences between the 24 and 26 hour primary enrichment time points for the
22
environmental surfaces tested, therefore a 24 hour minimum enrichment time will be
23
recommended for these matrixes: stainless steel, sealed concrete and plastic.
24
25
The five false negative results with raw chicken (leg pieces) evaluated in the internal study
26
resulted in an investigation of protocol. It was determined that the contract laboratory
27
conducting the study used Demi Fraser with FAC brand X, which demonstrated low
28
productivity. Brand X had also been used to analyze the inclusive list, spinach, and cold smoked
29
salmon.
30
31
When the protocol for raw chicken was performed at the independent laboratory, using a
32
different brand Y, two lots of naturally contaminated raw chicken (leg pieces) analyzed showed
33
no statistical difference when compared to the reference method. Lot 1 of the naturally
34
contaminated raw chicken (leg pieces) had zero false negatives, while Lot 2 had two false
35
negatives.
36
37
To expand the robustness of the method to include multiple raw chicken matrixes, raw chicken
38
fillets were chosen and brand Z was used. The raw chicken (fillet) testing resulted in no
39
statistical difference when compared to the reference method, which highlighted the importance
40
of internally validating any method as a system within one’s own laboratory. This is why 3M
41
has always emphasized this advisory within our package inserts;
42
43
“
As with all test methods, the source, formulation and quality of enrichment medium
44
can influence the results.
Factors such as sampling methods, testing protocols, sample
45
preparation, handling, and laboratory technique may also influence results. 3M
46
AOAC Research Institute
Expert Review Panel Use Only
OMAMAN-29 D/ PTM Validation Report 111501
OMA ERP - June 2016
ERP Use Only